Airborne Rain Mapping Radar (ARMAR) Measurements Taken Onboard the NASA DC-8 during the TOGA COARE Intensive Observing PeriodEntry ID: COARE_cm_dc8.armar
Abstract: DATA ACCESS
The ARMAR data are available from the NASA GSFC DAAC via ftp from
The ARMAR team at JPL put together a list of ARMAR files that elicited the most interest at the Science Working Group Meeting in March 1994. The files are grouped by flight and reside in directories labeled with the dates on which the data ... was acquired.
TOGA COARE was a multidisciplinary, international research effort that investigated the scientific phenomena associated with the interaction between the atmosphere and the ocean in the warm pool region of the western Pacific. The field experiment phase of the program took place from 1 November 1992 through 28 February 1993 and involved the deployment of oceanographic ships and buoys, several ship and land based Doppler radars, multiple low and high level aircraft equipped with Doppler radar and other airborne sensors, as well as a variety of surface based instruments for in situ observations.
The NASA component of TOGA COARE, while contributing directly to overall COARE objectives, emphasized scientific objectives associated with the Tropical Rainfall Measuring Mission (TRMM) and NASA's cloud and radiation program.
Mission and Objectives: ARMAR was developed by NASA/JPL for the purpose of supporting future spaceborne rain radar systems, including the radar for the Tropical Rain Measuring Mission (TRMM) to be flown in the late 1990s. It flies on the NASA Ames DC-8 aircraft and is operated by JPL. Its primary goal in TOGA COARE was to measure the three-dimensional reflectivity of rainfall.
Instrument Geometry: ARMAR operates with the TRMM frequency and geometry, measuring reflectivity at 13.8 GHz in a cross-track scan +/-20 degrees from nadir along the flight track of the aircraft. Nadir-looking, non-scanning measurements can also be acquired.
Principles of Operation: ARMAR is a pulse compression radar. The digital controller causes the chirp generator to produce chirps with the selected length, spacing, and start frequency. In normal operation, the waveform is a linear, frequency modulated upsweep chirp with 4 MHz bandwidth and amplitude weighting for range sidelobe suppression. The chirps are up-converted to 13.8 GHz and amplified by a high power traveling wave tube amplifier (TWTA). The amplified chirp is then sent to the antenna system. A small amount of power is sent directly to the receiver through a calibration loop with 84.5 dB attenuation. The TWTA is operated in the non-saturated mode to maintain the desired chirp amplitude characteristics. The antenna system consists of a dual, linearly polarized scalar feed horn which illuminates a precision offset parabolic reflector. The signal is focused by the parabolic reflector and reflected by a flat, mechanically scanned elliptical reflector which scans the beam +/-10 degrees in the crosstrack direction. The reflector can also be pointed or scanned up to +/-10 degrees in the along track direction, if desired. Both transmit and receive polarizations can be varied on a pulse to pulse basis, allowing a combination of like- and/or cross-polarization data to be collected.
The signal reflected from the rain is collected by the antenna and then amplified by a low noise amplifier (LNA). Following the LNA, the received signal is down-converted to the 70 MHz intermediate frequency (IF). Here, the signal is split into radar and radiometer signals. The radar signal is passed through a programmable attenuator before IF amplifiers and filters. In the final stage, the signal is down-converted to baseband (offset video) where it is digitized by a 12-bit, analog/digital converter (ADC) at a rate of 10 MHz and recorded. The radiometer signal is acquired during a short time within each interpulse period after return from the transmitted pulse has reached zero. This signal is integrated in analog circuitry, sampled every 10 ms, averaged, and recorded.
The ARMAR dataset is level 1B (calibrated and earth located). The ARMAR data have an approximate volume of 4 GB and a typical file size of up to 10 MB. The ARMAR file naming convention reflects the julian day and the time of the measurements and are of the format "ddhhmm.ARM."
Data Format: The ARMAR files are being archived in their native binary format and will eventually be superseded by HDF formatted files. Software is provided to convert the ARMAR data to NCAR's DORADE format. ARMAR files in DORADE format will contain single polarization, doppler data.
Description of ARMAR native format:
Parameters held in the first 80 bytes following an "#A"
param.: format: units: description:
prf 2-byte-int. Hz radar pulse repetition frequency
dat_type " - radar data type- see Table 2
spare0 " - not used (was radar "gate" mode)
no_av " - no. radar pulses read from original data
nbin " - no. samples in arrays
dt " s x10 range sample interval (x15 = meters per pixel)
no_av1 " - no. pulses actually averaged in pulse 1 power
no_av2 " - " pulse 2 power (2nd polarization)
spare1 " - not used (was pulse "id")
spare2 " - not used (was "nskip")
no_sumc1 " - no. pulses actually averaged in doppler 1
no_sumc2 " - " doppler 2 (2nd polarization doppler)
no_sumr " - no. pulses accumulated in lag-2 correlation
v_offset " m/s x 100 offset measured & applied to doppler
v_predict " " offset otherwise predicted from INS
n_miss " - no. radar pulses lost to data system errors
az1 4-byte-float deg. antenna azimuth at start of accumulation
az2 " " " at end of accumulation
el " " antenna elevation (aft is positive)
tb " K radiometer brightness temperature
time 8-byte-double s UT seconds
r0 2-byte-int. m range to first pixel below aircraft
npulse " - no. pulses to end of scan (1 is last pulse)
x " x 10000 along track cartesian antenna vector
y " " cross-track component
z " " zenith component
pol1 " - polarization 1: 1=HH, 2=VV, 3=HV, 4=VH
pol2 " - polarization of pulse 2: "
day " - Julian flight day (1 = 1 Jan 1994)
rcm " - radiometer calibration mode
scanmode " - ant. scan: 0=bowtie, 3=retrace, >3=fixed
spare3 " - not used
spare4 " - not used
(End of Table 1)
Interpretation of "ahd.dat_type" from Table 1
1 Single polarization, no doppler: read nbin samples of dBZ into
2 Dual polarization, no doppler: read nbin samples into z1, then
nbin samples into z2.
3 Single polarization doppler: read nbin dBZ values into z1, nbin
m/s values into velocity array v1, then nbin m/s samples into
doppler width array w1.
4 or 5 Dual pol. doppler: read nbin samples each into z1, v1, w1, z2,
v2, and w2. Polarizations are given in "ahd.p1" and "ahd.p2".
Type 5 normally implies cross-pol data for z2. Type 4 normally
implies HH/VV polarizations.
8 Single pol. noise floor: read nbin samples of mean noise into n1
array, and nbin samples of noise variance into nv1.
9 Dual pol noise floor: read nbin samples each into n1, nv1, n2,
nv2. These pol's should be paired with subsequent type 2, 4, or
5 dual polarized radar data.
note: z1, z2, v1, v2, w1, w2, n1, n2, nv1, nv2 should all be allocated as 400
Documentation: Two documents are available to assist users in reading and understanding ARMAR data: The "Quick Reference Guide", included with this distribution (ascii file "quickref.txt"), and the more comprehensive "User's Guide", available in this directory in file "user.ps" (see Section 8.1). The Quick Reference Guide describes the JPL internal format, how to read it, and describes software that is available to assist the user. The User's Guide provides a description of the hardware and its operating modes, data collection, processing, and calibration, and data quality assessment.
Browse Products: Color Post-Script images of selected flight segments reside in directory armar/armar_images. Images show nadir reflectivity as a function of height along with brightness temperature as a function of cross-track position. Each image represents about 10 minutes of data. The file names follow the dddhhmm.ps convention indicating the day (ddd) and approximate start time (hhmm) of the plot. Images can be viewed using any post-script viewer (i.e., pageview, ghostview, etc.). No doppler or cross-polarized data are plotted.
Software: The DAAC distributes read and conversion software that was provided by the data producers at JPL: - "read_arm.c" Code to read ARMAR data and display it to the terminal - "arm2dor.c" Code to convert ARMAR data from its native binary format to DORADE format
Data Set Citation
Dataset Originator/Creator: TOGA COARE
Dataset Title: Airborne Rain Mapping Radar (ARMAR) Measurements Taken Onboard the NASA DC-8 during the TOGA COARE Intensive Observing PeriodOnline Resource: ftp://disc1.gsfc.nasa.gov/data/toga_coare/aircraft/nasa_dc8/armar/
Start Date: 1993-01-01Stop Date: 1993-02-28
Distribution Media: On-line
Durden, S., A. Tanner, W. Wilson, F. Li, E. Im, and W. Ricketts, 1992: The
NASA/JPL airborne rain mapping radar (ARMAR). Proc. 11th International
Conference on Clouds and Precipitation, Montreal, 1013-101.
FIRE Project Office, 1993: Mission Summary Reports, TOGA COARE, NASA
Langley Research Center, Mail Stop 483, Hampton, VA 23666.
FIRE Project Office, ... 1994: NASA/TOGA COARE Science Data Workshop II,
Proceedings of a workshop held in Albuquerque, New Mexico, March
15-17, 1994. NASA Langley Research Center, Mail Stop 483, Hampton, VA
Jet Propulsion Laboratory, 1994: Quick Reference Guide for ARMAR TOGA
COARE Data Set. California Institute of Technology, Pasadena, CA
Jet Propulsion Laboratory, 1994: User's Guide to ARMAR TOGA COARE
DATA, Version 4.0. California Institute of Technology, Pasadena, CA
NASA TOGA COARE Project Office, 1994: NASA/TOGA COARE Science Data
Workshop II Proceedings, Albuquerque, New Mexico, March 15-17, 1994,
NASA Langley Research Center, Mail Stop 483, Hampton, VA 23666, 4 pp.
Tanner, A., S. L. Durden, R. Denning, E. Im, F. K. Li, W. Ricketts, and
W. Wilson. Pulse compression with very low sidelobes in an airborne
rain mapping radar. IEEE Trans. Geosci. Remote Sensing, in press.
TOGA COARE International Project Office (TCIPO), 1992: TOGA COARE
Operations Plan, Working Version September 1992. University
Corporation for Atmospheric Research, Boulder, CO 80307, 138 pp.
TOGA COARE International Project Office (TCIPO), 1993: TOGA COARE
Intensive Observing Period Operations Summary. University Corporation
for Atmospheric Research, Boulder, CO 80307, 505 pp.
TOGA COARE International Project Office (TCIPO), 1994: Summary Report
of the TOGA COARE International Data Workshop, Toulouse, France, 2 -
11 August 1994, University Corporation for Atmospheric Research,
Boulder, CO 80307, 170 pp.
Webster, P.J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean-
Atmosphere Response Experiment. Bull. Am. Meteorol. Soc. 73, 1377-1416.
World Climate Research Programme (WCRP), 1985: Scientific Plan for the
TOGA Coupled Ocean-Atmosphere Response Experiment. WCRP Publications
Series, No. 3 Addendum, World Meteorological Organization, Geneva, 96 pp.
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